Traffic protection apparatus



A. J. SORENSEN TRAFFIC PROTECTION APPARATUS Sept. 11, 1951 2 sheets-sheet 1 Filed Dec. 11, 1947 1P l V V 525 A A n JNVENTOR.

Sept 1 A. J. SORENSEN 2,567,897

TRAFFIC PROTECTION APPARATUS Filed Dec. 11, 1947 2 Sheets-Sheet 2 Permeabik'y W OPfiay pae'n.

MW @wwy,

\ INVENTOR.

J wwmgwm Patented Sept. 11, 1951 UNITED STATES PATENT com-cs 2 ,567,897 7 seems P tQTJ-E N erm teri Andrew J. Sorensen, Edgewood, Pa., assignor to The Union'switch & Signal Co'mpa-"ny;Swiss! vale, Pa., a corporation of Pennsylvania; epp cei ee DPPPF 11, 9 7. i s ie N @1422 16 Qlaims. (01. 24692 19) 1 .MY i vent on l t 9 ams ts i91 ep Waws and pec cularlv el c H asnetic m n-s loca es b t se b ot onnss esl' wi h ack rails of a retch of ailway tr k i pr con ro ling traf c overni g ap aratu c o d: as the str tch o a lwa track s cl ar o cu ied b a w o ain- T s applic io fl ii uatio -i -part .0: my earlier ap l ca io or Let e s P tac o the United Stat Seria 886 fil A21 1 2. 1947, for Traffic Protection Apparatus, now an-v lpned- 2. 3 o he r s l c tion o m 1. 9 to i 2, and p t vely 9 the ea ie @92 i a In ai wa ,r tion appa a u it o d th t "t ack si c s for tracks o er which train movements are infrequent, .such as crossover tracks and spur tracks, at timeshave s shun i g en itivity at s me 1Qa= l' he Phras l. end n a es tra k 91 et e m l ed- I111 m9 in tances it is therefore desirable to use ther means in ase tien o a ins as o t ees ii :i d t tin the'rr sle. be a 9 t a e n a st tch 0 track.

' It w l that magnet zable bodies aiiec the c t ib ti of ma netic a x su th fie o th e s ca casses ma I a en found that a e 59 2 l'Qn or steel suc as in a rai way their,

' h e r i his resid a ma ne sm 'AQF-Qtdihflh one i e er '9'? m wrestles s th Prov o lectro a n i par isaie an given st tch of fla trac havin ma net.- ',izabl e core mat ial ar anged so that the d stribution of the magnetic flux through the sore mat ia va y a ar or trainloii the stret track for ef ectin ecrrespo din ,coh rol 9; traits rn n par u A et r f atur o m i ve t i the o is on is e ic y o era i mean f tin clo es? icirwit con ol -i the a pa a us! :.I h descr b thr e for s 0; apparatu o bodyms m invention, an shall h n nojmt out the lprel ie ts es the o e a ms- In the acc mpa y n drawings; ,F .1 a iasrasnmatic view s owin 91 tom o abee aws emhsmyzmg my invent n in which elec roma ;netic app ratus loca edbe wee t e ra ls o a cros ver tr sh and v es with means for periodically varying the mash? th ou h ts ma r a an mas d so th a a 9 t am on h s cr sswe tr ck wi l produce ac nstentch e in the mean tic flux t ressh its we mat ria Eis- 2 a charm t v ly, a?

ssr s J Y 9 matic view showing a modified term of the apparatus oi 1', in whichth'fiiui fihiou'gh the core material is'constan-t until acar or at rives butalternating cur-rem controlled by the core materialist periodicalliv'varied; Fig. 3 a View showing, by a ciirve ,"the relationship be tween flux derisityand permeability of the magnetiz'abie"cor"e' malterial; and Fig.' 4"is' a diagraiiimatic View showing another modified form of the apparatus of in which a magnetic amplifying arrangement is provided.

"Similar reference characters refer to similar parts in each of the views. W

Referring fi'rst'to Fi gf-l, a stretch of railway is shown comprising two main tracks, designated by the referencec h'jar'acters and ZTfint'ercon nected by a cross-over track 3T throughhandoperated. switches IW and 2-W. Tracks IT and 2T are divided by insulated joints 4 to form sec tions -a'-b and (iv-d; respectively, including switches lW and 2W, respectively.

' Each of these track sections may be provided with a track circuit, as shown for-section 00-17, which includes a suitable source of current, such as a battery 5 connected across the rails adjacent one end of the section, and a track relay, designated by the reference character IR, connected across the rails adjacent the other end of the section, and which also includes an adjacent portion of track 31, as is common practice.

A signal [G is shown for governing traffic movements into section a-'- -b, and asignal 2G is shown for governing :trafiic movements into section c-=-d. Each of these signals may be of any suitabletype, such, .for example, as the sema; pho reor searchlight type;

"Two bars, designated by the reference char-ac.- ters I}? and 2P, of magnetizable material having high permeability, are located side by side. but spaced a short distance from each other, between and parallel to theraiis of the portion of track 3T which is included in the track circuit for sec: tion a-b. In an actual test which made of this invention, the bars or cores 1P and 2? vwere laminated; were on the order of eight inches in length, and were spaced three inches apart. Threeseparate coils ii, 21' and 31' are wound around-bar or core 1 1?, and three coilsti, 5i and 62', similar respectively to coils I- i, 2i and 32' of so e 1 a WQJW s ress??? Q s re s Win i i s l nd o cor iP and 2 E P??- Ji e an a e qn t et iisr eee "di ect cur,- ,4 ,7 whi ls'il turn ene iz s t ain seesaw w nsin s 9ft power transformer A. Current from rectifier IE flows through winding Ii of core IP in a, direction which is opposite to the direction in which current flows through winding 42' of core 2P, and hence the adjacent ends of bars IP and 2P have opposite magnetic poles. The left-hand end of bar IP, as shown in the drawing, has a south pole, designated by the reference character S, whereas the adjacent end of bar 2? has a north pole, designated by the reference character N.

Windings 2i and 5i of cores IP and 2P, respectively, are also alike, andare energized in opposite directions with respect to each other, but are only alternately energized, through the front and back points, respectively, of a contact of a code transmitting device'CT, from a suitable source of direct current, such as a rectifier 2E, which is in turn energized from a secondary winding I of transformer A. Winding 22' is energized in the direction opposite to that in which winding Ii is energized, so that it cancels a portionof the flux produced by winding Ii, while windin 22' is energized. Similarly, winding 52 is energized in the opposite direction to winding 42, so that while winding 51' is energized, it cancels a portion of the flux produced by winding 42'. The apparatus is so proportioned that the flux density produced in bars IP and 2P by the current flowing in windings l2 and 42, respectively, is at a working point on a steep portion of the curve shown in Fig. 3. The current flowing in windings 2i and 51 is adjusted to lower the fiux density only enough to increase the permeability of bars IP and 2P, respectively, to near the peak of the curve shown in Fig. 3. The apparatus is also so proportioned that a car, upon passing over bars IP and 2P, will decrease the flux in one of the bars enough to increase the permeability of that bar to near the peak of the curve and will increase the flux in the other bar byv a similar amount and correspondingly decrease the permeability of that other bar.

Alternatin current is supplied by secondary .winding 8 of transformer A through windings 3i and 62 to amplifiers IM and 2M, respectively. The magnitude of this alternating current is in.- creased or decreased according as the impedance of windings 3i and 61 ,isdecreased or increased, respectively, by the increase or decrease, respectively, of the fiux in bars IP and 2P.

The output current from amplifier IM is supplied to a rectifier 31-11 which in turn energizes winding 9 of a code following polar stick relay BIR. The output current from amplifier 2M is supplied to a rectifier 4E which in turn energizes winding II] of code following relay BIR.

Movement of contacts II and I2 of relay BIR to the normal position, in which they are shown in Fig. l, is effected by energization of winding I0 of this relay, whereas movement of contacts II and I2 to the reverse position is effected by energization of winding 9 of relay BIR. If the current supplied to winding 9 of relay .BIR were of the same magnitude as that supplied to winding IU of this relay, the polar contacts II and I2 would remain in the position to which they were last previously operated.

, The flux is increased alternately in bars IP and 2P by the current flowing in windings 22' and Si, respectively, and hence the current is decreased alternately in windings 9 and I0, respectively, of relay BIR, so that contacts II and I2 of'relay BIR will be normally moving repeatedly 4 between their normal and reverse positions. A slow release signal control relay AIR will therefore be normally energized from a decoding transformer F, and contact I3 of relay AIR will be closed in a circuit for clearing signal IG. A similar contact of relay AIR will be closed in a similar circuit for controlling signal 2G.

Each of the rectifiers IE, 2E, 3E and 4E, rectifier 5E shown in Fig. 2, and rectifiers 6E and IE shown in Fig. 4 may be of the well-known copper oxide type comprisin four half-wave units such, for example, as units I6, 26, 3e and 4c, of rectifier IE, with the low resistance direction of each unit as indicated by its arrow head.

Primary winding I5 of transformer A is energized from a suitable source of alternating current, having terminals BX and CK, which may perhaps have a frequency of the order of 500 to 1000 cycles per second.

Referrin now to Fig. 2, another arrangement for controlling relay AIR by variations in flux in bar IP and 2P is here shown.

Windings Ii and 42' are here energized in opposite directions by direct current from a bat tery Q. Windings 32' and 62' here constitute two arms of a bridge, and two variable resistors I1 and I9 constitute the other two arms of the bridge. Alternating current of suitable frequency such, for example, as 500 to 1000 cycles per second is supplied to the bridge from a source having terminals BX and CK.

An amplifier M is connected across the midpoints I6 and ill of the bridge through a filter L which is tuned to the frequency of the alter nating current source. Primary winding 20 of a transformer IF is connected across the opposite side of amplifier M.

A neutral code following relay I is controlled 7 from the secondary winding 2I of transformer IF through rectifier 5E. Relay AIR is here controlled by contacts 22 and 23 of relay I through a decoding transformer F.

A front contact 24 of a code transmitting device CT is here connected across resistor I9 in one of the arms of the bridge. The apparatus is so proportioned that the impedances of windings 3i and 61' are equal when contact 24 of device CT is open, and resistors I1 and I9 are adjusted to have equal resistances. Therefore, when contact 24 of code transmitter CT is open, the bridge is normally balanced, so that there is no voltage drop across the midpoints I6 and I8 of the bridge, and hence relay I is deenergized. When contact 24 of code transmitter CT closes, however, the bridge becomes unbalanced, so that relay I becomes energized.

Contacts 22 and 23 of relay I therefore'normally repeatedly close alternately at their front and back points, in response to the operation of contact 24 of code transmitter CT, so that r'elay AIR is normally energized and its contact I3 is normally closed in the control circuit for signal IG shown in Fig. 1, and a similar contact is closed in a control circuit for signal 2G.

When a car or train passes over bars IP and 2P, causing the flux in one bar to increase and in the other bar to decrease, the bridge is constantly unbalanced, so that relay I is constantly energized, and therefore relay AIR is deenergized and its contact I3 is open in the signal IG control circuit;

' Referring now to Fig. 4, the circuits for windings I 2', 22', 4'2 and 52' are here the same as in Fig. l. Windings 3i and Bi, instead of being energized by the same secondary winding '8 of transformer'A 5. as in-Fig. 1, are. here energized by separate secondary windings 21 and 29, respectively. A magnetic amplifying arrangement-is provided, including magnetic amplifiers AIM and A2M. Each of the amplifiers AIM and A2M comprises a magnetizable core 11, an input winding 32, a bias winding 36, and an output winding 39.

A resistor 33 is connected between positive terminal 30 of rectifier IE and negative terminal 34 of rectifier 6E.

Input windings 32 of amplifiers AIM and AZM are connected in series with each other across a common terminal 3| which is connected with the opposite terminals: 28 and 35 of rectifiers 6E and IE, respectively, and'a midpoint of resistor 33. Bias windings 36 of amplifiers AIM and A2M are energized in series with each other from rectifier IE. l I I Winding 9 of relay BIR is energized from secondary winding 38 of transformer A through output winding 39 of amplifier AIM and rectifier 3E. Winding III of relay BIR is energized from secondary winding 31 of transformer A through output winding 39 of amplifier MM and rectifier 4E.

Having described, in general, the arrangement ofthe various parts of apparatus embodying my invention, I shall now describe the circuits and operation in detail.

As shown in the drawings, all parts of the apparatus are in the normal condition, that is, each of the switches IW.and 2Wis in the normal position for a train movement along track IT or 2T, respectively; each of the signals IG and 2G is indicating proceed; code transmitting devices CT are. repeatedly moving their contacts alternately to their energized and deenergizedposi: tions; windings I1 and 42 are constantly energized in opposite directions with respect to each other; windings 2i and Si in Figs. 1 and 4 are repeatedly energized alternately, and in opposite directions with respect to current in windings .Ii and 41, respectively; alternating current is supplied to amplifiers IM and 2M through windings 32 and 62, respectively, in Fig. 1, and is supplied to the bridge in Fig. 2; input windings 32 of amplifiers AIM and A2M'in Fig. ,4 are energized from secondary windings 21 and 29 of transformer A through windings 3i and 61'; relay BIR in Figs. 1 and 4 is repeatedly closing its contacts II and I2 alternately in their normal and reverse positions; relay I in Fig. 2 is repeatedly closing its contacts 22 and 23 alternately at their front and back points; and relays AIR are constantly energized.

I shall assume that, with apparatus arranged as shown in Fig. 1, a trainman reverses switches IW and 2W, so that a train may proceed over track 3T. I shall assume further that a car or train, when it passes over bars IP and 2P, adds to the fiux in bar IP produced by winding Ii, and decreases the flux in bar 2P produced by winding 4i.

The circuit by which windings Ii and 41' are energized passes from rectifier IE, through winding 4i and winding Ii in the opposite direction, back to rectifier IE, causing the left-hand end of bar 2?, as shown in the drawing, to have a north pole N, and the adjacent left-hand end of bar IP, as shown in the drawing, to have a'south pole S.

Code transmitter CT is constantly energized from a suitable source of current having termi= nals B and C, and hence its contact 25 is repeatedly closing alternately at its front and back points. With contact 25 of device CT closed at 'ese'asov cult passing from rectifier 2E, through the front point of contact 25, and winding 2i, back. to rectifier 2E. When contact closes at its back point, winding 51' is energized by a circuit passing from rectifier 2E, through the back point of contact 25, and winding 5i back to retifier 2E.

However, with the flux in bar IP increased, and with the flux in bar 2]? decreased, due to the car or train, as assumed, the permeability of bar I will be lower than that of bar 2P, and hence the impedance of winding 3i will be lower than that of winding 61, so that the contacts of relay BIR will will be constantly closed in the reverse position. With contacts II and I2 constantly closed in one position, no alternating current will be generated in the secondary windin of tansformer F, and hence relay AIR will become deenergized, and its contact I3 will be open in the control circuit for signal IG, so that signal IG will indicate stop as long as the car or train remains adjacent bars IP and 2P. With the apparatus as shown in Fig. 2, windings Ii and 42' are constantly energized by current its front point, winding 21' is energized by a cir- 15 passing from battery Q, through a variable resistor 26, winding 4i, and winding Ii back to battery Q. Alternating current passes from terminal BX, through winding 32, point I6 of the bridge, and variable resistor H to terminal CX. Alternating current also passes from terminal BX, through winding 62, point I8 of the bridge, and variable resistor I9 to terminal CX. When contact 24' of code transmitter CT is open, the current flowing through these two circuit paths is the same, and hence there is no voltage drop between midpoints I6 and I8 of the bridge. Each time that contact 24 closes, however, current is shunted around resistor I9, causing a voltage drop to be produced across midpoint I6 and I8 for energizing primary winding 20 of transformer IF through amplifier M and filter L. 1

If a car increases the fiux in bar IP and decreases the flux in bar 2P, as previously assumed, however, the bridge will be permanently unbalanced as long as the car remains in the posttion to have this influence on bars IP and 2P, and hence transformer IF will be continuously energized, causing relay I in turn to be continuously energized, and therefore relay AIR will be deenergized and its contact I3 will be open in the circuit for signal IG, and a similar contact of relay AIR. will be open in a similar circuit for controlling signal 2G.

With apparatus as shown in Fig. 4, the circuit for energizing the input windings 32 of amplifiers AIM and MM from secondary winding 21 of transformer A passes from the left-hand end of winding 21, as shown in the drawing, through winding 3i of core IP, asymmetric unit Ie of rectifier 6E, terminal 28 of rectifier 6E, terminal 3|, input windings 32 of amplifiers AIM and A2M, resistor 33, terminal 34 of rectifier 6E, and asymmetric unit 2e of rectifier 6E, back to second ary winding 21 of transformer A. The circuit for energizing input windings 32 of amplifiers AIM and AZM from secondary winding 29 of transformer A passes from the left-hand end of winding 29, as shown in the drawing, through winding iii of core 2?, asymmetric unit Ie of rectifier 1E, terminal 30 of rectifier IE resistor 33, input windings 32 of amplifiers AIM and A2M, terminal 31, terminal 35 of rectifier IE, and asymmetric unit 2e of rectifier "IE, back to winding 29 of transformer A.

It will be noted that the voltages provided by secondary windings 21 and 29, in the circuits just traced, across resistor-33 and terminal 3| are opposed to each other, so that when these voltages are equal, no current will flow through input windings 32 of amplifiers AIM and A2M. These voltages are equal only during the, intervals when contact 25 of code transmitter CT is open at both its front and its back point.

When contact 25 is closed at its front point, the impedance of winding 31' is higher than that of winding 62', so that current from secondary winding 29 then flows from resistor 33 through input windings 32 to terminal 3I. The flux produced in core y of amplifier A2M by its input winding 32 is now in the same direction as the flux produced by bias winding 36 of amplifier A2M, whereas the flux produced in core 11 of amplifier AIM by its input winding 32 opposes the flux produced by bias winding 36 of amplifier AIM. The magnetic flux in core 1; of amplifier AZM, is therefore of higher magnitude than the fiux in core y of amplifier AIM, so that winding II] of relay BIR is energized from secondary winding 31 of transformer A by current of higher magnitude than winding 9 of relay BIR is energized from secondary winding 38 of transformer A. The circuit for energizing winding I8 from one half of the alternating current wave passes from the left-hand terminal of secondary winding 31 of transformer A, as shown in the drawing, through output winding 39 of amplifier A2M, asymmetric unit Ie of rectifier 4E, winding ID of relay BIB, and asymmetric unit 26 of rectifier 4E back to secondary winding 3'1. The circuit for energizing winding -I by the opposite half wave from secondary winding 31 can be readily traced on the drawing. Contacts I I and I2 of relay BIR therefore become closed in their normal positions.

When contact 25 of code transmitter CT is closed at its back point, the impedance of winding 61 is higher than that of winding 31', so that currentfrom secondary winding 21 of transformer A then .flows from terminal 3I through input windings 32 of amplifiers AIM and AZM to resistor 33. The flux produced in core y of ampli- 1fier AIM by its input winding 32 is now in the same direction as the flux produced by bias winding 36 of amplifier AIM, whereas the flux produced in core y of amplifier AZM by its input winding 32 now opposes the flux produced by bias winding 36 of amplifier AZM. The magnetic flux in core y of amplifier AIM is therefore of higher magnitude than the flux in core 11 of amplifier A2M, so that winding 9 of relay BIR is now energized from secondary winding 38 of transformer A by current of higher magnitude than winding I0 of relay BIR is energized from secondary winding 31 of transformer A. Contacts II and I2 of relay BIR therefore become closed in the reverse position.

If a car or train increases the magnetic flux in bar IP and decreases the magnetic flux in the bar 2P, as previously assumed, the impedance of winding 62' will be constantly higher than that of winding 31', so that contacts I I and I2 of relay BIR will be constantly closed in their reverse or right-hand position, as shown in the drawing.

Relay AIR, controlled by relay BIR, as shown in Fig. 1, will therefore be deenergized, causing signals IG and 2G to indicate stop.

Although I have herein shown and described only three forms of apparatus embodying my invention, it is understood that various; changes and modifications may be made therein within the scope ofthe appended claims Without departing from the spirit and scope of my inven tion.

Having thus described my invention, what I claim is:

. 1. In traffic protection apparatus for a stretch of, railway track including a railway signal, the combination comprising, two bars of magnetizable material having high permeability and arranged parallel to each other between the rails of said stretch of track, a magnetizingcoil for each of said bars energized by direct current and arranged so that a given end of one of said bars is the north pole of a magnet and the adjacent end of the second bar is the. south pole of a magnet and the opposite or south pole end of said first bar is adjacent the rforth pole of the second bar, a second coil for each of said bars energized by alternating current, coding means for periodically varying the alternating current flowing in said second coils, and a code following relay controlled by said periodically varied alternating current flowing through said second coils for controlling said signal to display a proceed indicae tion if said track is unoccupied but controlling said signalto display the stop indication if a train passes over said parallel bars.

2. In traflic protection apparatus for a stretch of railway track including a railway signal,.the combination comprising, two bars of magnetizable material having high permeability and located side by side adjacent and parallel to each other between the rails of said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other bar to the same degree in the opposite direction, a winding around each of said'bars and eachof said windings energized by alternating current, means for periodically varying the magnitude of the alternating current flowing through said windings, and means controlled by said alternating current flowing through said windings for controlling said signal to display a proceed indication if said track is unoccupied but controlling said signal to indicate stop in response to a car or train on said stretch of track adja cent said parallel bars.

3. In trafiic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located ads jacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, other means for periodically varying alternately the magnetic flux in said bars, and a code following relay controlled by said periodic variations of magnetic flux to periodically close and open its contacts and controlled by the magnetic flux in said bars as influenced by a railway vehicle on said stretch of track adjacent said bars to constantly close its contacts.

4. In traffic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, means for pe riodically reducing the magnetic flux in said bars alternately, and a code following relay controlled to periodically close and open its contacts in response to said reductions in magnetic flux and to constantly close its contacts in response to the magnetic flux in said bars as influenced by 9 a railway vehicle on said stretch of track adjacent said bars.

5. In traflic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a winding around each of said bars, and trafiic governing means controlled by variations in alternating current supplied through said windings in accordance with variations in magnetic flux in said bars produced by a railway vehicle on said stretch of track adjacent said bars.

6. In traffic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a winding around each of said bars, a first and a second resistor, a bridge including one of said windings in series with one of said resistors as one side of the bridge and including the other of said windings inseries with the other of said resistors as the other side of said bridge, means for passing alternating current through said two sides of said bridge in multiple with each other, means for periodically varying the alternating current passing through one of said resistors, anda neutral code following relay controlled by a circuit connected across the mid points of said bridge one of which is between one of said windings and the resistor with which it is in series and the other of which is between the other winding and the other resistor and periodically energized in response to said variations in alternating current but constantly energized in response to change in magnetic flux in said bars produced by a railway vehicle on said stretch of track adjacent said bars.

'7. In traffic protection apparatus for a stretch of railway track, the combination comprising, a,

pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, means for periodically reducing the magnetic flux in said bars alternately, a control winding around each of saidbars, and a polar biased code following relay having two windings one of which upon becoming energized by alternating current passing through one of said control windings closes the contacts of said relay in a normal position and the other of which upon becoming energized by alternating current passing through the other of said control windings closes the contacts of said relay in a reverse position in response to variations in magnetic flux in said bars.

8. In combination, two bars of magnetizable material having high permeability and located side by side adjacent and parallel to each other, a magnetizable coil for each of said bars each energized by unidirectional current and arranged so that a given end of one of said bars is the north pole of a magnet and the adjacent end of the second bar is the south pole of a magnet and the opposite or south pole end of said one bar is adjacent the north pole end of said second bar, a second coil for each of said bars each energized by alternating current, coding means for periodically varying the alternating current flowing in said second coils, indication means.

10 and a code following device controlled by said alternating current in said second coils for controlling said indication means to display normally a given indication but to display a different indication when there is magnetizable body adjacent said bars.

9. In combination, two bars of magnetizable material having high permeability and located side by side adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other bar to the same degree in the opposite direction, a winding around each of said bars and each of said windings energized by alternating current, means for periodically varying the magnitude of the alternating current flow-'- ing through said windings, indication means, and means controlled by said alternating current after leaving said windings for controlling said indication means to display normally a given in-, dication but to display a diiierent indication when there is a magnetizable body adjacent said bars.

10. In combination, a pair of bars of magnetizable material located adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, other means for periodically varying the magnetic flux inv said bars, and contacts controlled by said periodic variations of magnetic flux to periodically close and open and controlled by the magnetic flux in said bars as influenced by a magnetizable body adjacent said bar to remain constantly closed.

11. In combination, a pair of bars of magnetizable material located adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, means for periodically varying the magnetic flux in said bars alternately,- a winding around each of said bars, and indication means controlled by variations in alternating current supplied through said windings in accordance with said periodically varied magnetic flux to display normally a given indication, but controlled to display a given different indication in response to modification of said flux by a'magnetizable body adjacent said bars.

12. In combination, a pair of bars of magnetizable material located adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a winding around each of said bars, a first and a second resistor, a bridge including one of said windings in series with one of said resistors as one side of the bridge and including the other of said windings in series with the other of said resistors as the other side of said bridge, means for passing alternating current through said two sides of said bridge in multiple with each other, means for periodically varying the alternating current passing through one of said resistors, and contact means controlled by a circuit connected across the midpoints of said bridge one of which is between one of said windings and the resistor with which it is in series and the other of which is between the other winding and the other resistor and periodically operated in response to said variations in alternating current but constantly operated in response to change in magnetic flux in said bars produced by a magnetizable body adjacent said bars.

' 13. In combination, a pair of bars of magnetizable material located adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, means for periodically reducingthe magnetic fiux in said bar alternate- 1y, a control winding around each of said bars, and a polar biased relay controlled by alternating current passed through said control windings as influenced by the periodic reductions in magnetic flux in said bars to close its contacts in a normal or a reverse position alternately and to close its contacts constantly in the normal or the reverse position in response to a magnetizable body adjacent said bars. v

14. In traffic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a control'W-inding around each of said bars, a magnetizable core, a magnetizing coil around said core, a second magnetizable core, a second-magnetizing coil around said second core, a circuit including a source of current and the control winding for one of said bars and also including asymmetric means and said first and second magnetizing coils all in series, a second circuit including a source of current and the control winding for the other bar and also including asymmetric means and said first and second magnetizing coils all in series, an output winding around said first core, a second output winding around said second core, and trafiic governing means controlled by said first and second output windings.

' 15. In trafiic protection apparatus for a stretch of railway track, the combination comprising, a pair of bars of magnetizable material located adjacent said stretch of track, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a control winding around each of said bars, a, magnetizable core,

around said second core, a circuit including a source of current and the control winding for one of said bars and also including said first and second magnetizing coils all in series, a second circuit including a source of current and the control winding for the other bar for passing current through said first and second magnetizing coils in the opposite direction to current in said first circuit, and traflic governing means controlled by magnetic flux produced in said magnetizable cores by said first and second circuits.

16. In combination, a pair of bars of magnetiz able material located adjacent and parallel to each other, means for constantly magnetizing one of said bars in a given direction and for constantly magnetizing the other of said bars in the opposite direction, a control winding around each of said bars, a magnetizable core, a magnetizing coil around said core, a second magnetizable core, a second magnetizing coil around said second core, a circuit including a source of current and the control winding for one of said bars for passing current in a given direction through said first and second magnetizing coils, a second circuit including a source of current and the control winding for the other bar for passing current in the opposite direction through said first and second magnetizing coils, a bias winding around each of said cores, means for energizing said bias windings for producing magnetic flux in said first core in the same direction as the flux produced by said first circuit and for producing magnetic flux in said second core in the same direction as the flux produced by said second circuit, and indication means controlled by the magnetic flux produced in said magnetizable cores.

ANDREW J. SQRENSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,007,715 Glock July 9, 1935 2,032,810 OMeara Mar. 3, 1936 

